1. Field of the Invention
The present invention relates to a susceptor device, manufacturing apparatus of epitaxial wafers and a method of manufacturing epitaxial wafers.
2. Description of Related Art
Methods of manufacturing epitaxial wafers have been known to include growing epitaxial films in vapor phase onto surface of the wafers (see e.g., Document 1: JP-A-2000-269137).
Document 1 discloses that a back surface of a susceptor is supported by a quartz support shaft at three points. Above and below the susceptor supported by the support shaft, heaters for heating the susceptor and wafer with radiation heat are provided, and such heaters include halogen lamps and the like.
However, in the structure disclosed in Document 1 in which a non-mounting surface of the susceptor is only peripherally supported by the support shaft, radiation light from the heaters reaches the susceptor from the front, back, left and right and concentrates on the central portion of the non-mounting surface of the susceptor. Accordingly, the portion of the susceptor corresponding to the center of the epitaxial wafer (“center” means a single center point) and its neighborhood (hereinafter referred to as “susceptor-center-corresponding portion”) exhibits higher temperature than the surrounding portion. Consequently, the epitaxial film at the central portion of the epitaxial wafer becomes much thicker than at the surrounding portion. In other words, nonuniformity in the thickness is increased at the central portion of the epitaxial wafer (“central portion” means a portion corresponding to substantially a circle described around the center of the epitaxial wafer with the diameter of approximately A/2 where the diameter of the epitaxial wafer is set at A). The “nonuniformity in the thickness at the central portion of the epitaxial wafer” is hereinafter referred to as “central thickness nonuniformity.”
One possible method to reduce such central thickness nonuniformity is to greatly reduce the amount of reaction gas used in vapor-phase growth of the epitaxial film.
However, the reduction in the amount of the reaction gas can improve the central thickness nonuniformity, but invites abnormal growth on the back surface of the epitaxial wafer, so that nanotopography is deteriorated.